I first came across the concept of unlearning in Swieringa and Wierdsma's
1992 'Becoming a Learning Organization' (ISBN 0 201 62753 1) and found it
very useful.

As I understand their take on the concept, at the personal level it has to
do largely with the gap between espoused theory and theory in use. We
learn new ideas or new frames but continue to behave in the old way. How
do we unlearn the visceral level behaviours that undermine the integrity
with which we act? Have you ever tried to drop a bad habit?

At an organisational level, it has to do with the trauma experienced as
people find that what used to be accepted norms or what used to be
rewarded (eg unquestioning obedience) is now a barrier to their progress.
Learning and unlearning go together, but its the unlearning that is
painful.